Linquan Sun,Hongdong Yu,Fancheng Meng,Tao Qi,Shili Zheng,Yihe Peng,Lina Wang
Niobium consumption has burgeoned owing to the increasing application of niobium in critical industries, including the aerospace and oil and gas industries. Conventional metallurgical technologies and separation methods for niobium extraction use highly concentrated HF, which is hazardous to both humans and the environment. A solvent extraction system comprising trioctyl tertiary amine (N235) and 4-methyl-2-pentanone (MIBK) that can extract and separate niobium from an oxalate-containing H 2 SO 4 solution is proposed in this paper. Niobium solutions tend to contain titanium and iron impurities; therefore, the effects of various conditions on the separation of the three elements were investigated. The extraction mechanism and thermodynamics of the process were also examined. Over 82% niobium was extracted at an organic-to-aqueous phase ratio of 1:1 and the H + concentration of 8.29 mol/L using an organic phase with 50 vol% N235 and 50 vol% MIBK as the extractants at 20 °C. Only 18.4% titanium and 3.35% iron were co-extracted. Two stripping processes, both of which further separated niobium and titanium, are also proposed herein. The possible composition of the niobium-containing extraction complex was [(R 3 NH)·NbO(C 2 O 4 ) 2 (H 2 O) 2 ], as supported by a Fourier transform infrared spectroscopy (FT-IR) analysis and ultraviolet–visible (UV–vis) spectrophotometry . The extraction mechanism was inferred to be the association of R 3 NH + in N235 with the [NbO(C 2 O 4 ) 2 (H 2 O) 2 ] − from the acidic niobium-containing solution, and the stripping mechanism was concluded to be anion exchange. The enthalpy change (∆H o ) of the extraction system was −11.0 kJ/mol at 288.15–313.15 K, which indicated that niobium extraction from the H 2 SO 4 solution with oxalate using N235 and MIBK was an irreversible exothermic process.
A fluoride-free solvent extraction method for niobium separation in leached sulfuric mother liquor of ilmenorutile was proposed in this paper. The extraction system comprising trioctyl tertiary amine (N235) and 4-methyl-2-pentanone (MIBK) demonstrated good extraction efficiency and selectivity of niobium over titanium and iron impurities in sulfuric acid–oxalate solutions. Details of extraction, scrubbing, and stripping processes were investigated herein, and its practical effectiveness in both batch and multi-stage simulated counter-current modes was verified. Over 73.8% niobium was extracted under optimum conditions, and only 2.8% titanium and 1.7% iron were co-extracted. The recovery of niobium reached 99.1% in the four-stage simulated counter-current extraction tests. In the three-stage simulated counter-current stripping tests, the stripping efficiency of niobium reached 99.7% with 2.0 mol/L HNO 3 . Qualified niobium oxide products were prepared. The enthalpy change, entropy change, and the standard Gibbs free energy change (Δ H o , Δ S o , and Δ G o , respectively) corroborated the exothermicity, orderliness, and spontaneity of the reaction. The possible composition of the extraction complex was [NbO(C 2 O 4 ) 2 (H 2 O) 2 ] − , as supported by a Fourier transform infrared spectroscopy and ultraviolet–visible spectrophotometry. The extraction mechanism was inferred to be the outer-sphere complexation through physical binding which was the association of R 3 NH + in N235 with the [NbO(C 2 O 4 ) 2 (H 2 O) 2 ] − . A preliminary mass balance indicated that 203.92 g Nb 2 O 5 was generated from 1000 g raw material ilmenorutile.
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